The batteries which can show their remaining capacity in today's market, such as Duracell®, they have a liquid crystal linking positive and negative poles, which is between the surface of battery and its packaging wrap. The remaining capacity can be shown by liquid crystal; however, liquid crystal does not have an illumination function, so customers cannot watch the remaining capacity in a dark environment. China patent 200720032012 discloses a battery that provides not only a power supply but also illumination. There is a light-emitting diode linking the battery's positive pole and negative pole. And a light-emitting diode is incorporated with the battery. The disadvantage of this patent is that it will cause the battery capacity to decrease if we don't change the battery's size, because incorporating the light-emitting diode and the battery will cause the light-emitting diode to occupy the inner space of the battery. The production craft of the battery is different and cannot contain the same power as before.
China patent 200610114507.5 discloses a self-illuminating battery which can be charged. It is in fact a light and is largely different from a common battery.